What Experts Really Think About Diet Soda

Growing up, Olivia Dreizen Howell, 39, “lived on” diet soda. So did her family. At a family reunion in 1996, everyone sported T-shirts with their shared surname in Diet Coke-can font. “We drank Diet Coke, Diet ginger ale, and Diet Sprite like water—there was no difference in our household,” she says.

Like many, Howell believed that sugar-free soda was a benign choice. But the latest research casts doubt on that assumption, linking diet drinks to mood disorders, fatty liver development, autoimmune diseases, and cancer, to name a few. 

Before you pour your diet soda down the drain (a step one health expert does, in fact, recommend), know this about diet-soda research: the vast majority of it is observational—drawn from public-health records and long-term population studies—as opposed to the scientific gold standard of double-blind placebo-controlled studies. 

Here’s what we know so far about what diet soda might be doing to your health.

Diet soda is linked to a higher diabetes risk 

“Type 2 diabetes seems to be the strongest link” when it comes to diet soda and health risks, says Susan E. Swithers, a professor of neuroscience at Purdue University who researches diet soda's effects on metabolic health.“That seems to be a fairly consistent finding.” A 2023 study of nearly 106,000 people found that people who consumed more artificial sweeteners had a higher risk of Type 2 diabetes than people who didn’t eat or drink any.

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Earlier work by Swithers found that people who drink a lot of diet soda face increased risks for excessive weight gain, Type 2 diabetes, cardiovascular disease, and metabolic syndrome, a constellation of conditions which include excess body fat (especially in the middle), elevated blood sugar and blood pressure, and higher triglycerides — “all of which are risks for the development of Type 2 diabetes and heart disease,” says Dr. Barry Schuval, an endocrinologist at Northwell Health.

It's linked to worse heart health

Several studies have linked artificially sweetened drinks like diet soda to heart issues, particularly increased risks of stroke, coronary heart disease, and heart attacks. Most recently, a March 2024 study found that people who drank more than two liters of artificially sweetened beverages per week had a 20% higher risk of atrial fibrillation than people who didn’t consume sweetened drinks. “It’s important not to assume that low-calorie [diet drinks] are inherently healthy,” says Dr. Ningjian Wang, lead author and professor of endocrinology and metabolism at Shanghai Ninth People's Hospital in China.

Melissa Prest, a dietitian and spokesperson for the Academy of Nutrition and Dietetics (who was not involved in the study), emphasized that the observational nature of the study means we don’t know why this link occurred. Before leaping to any conclusions about whether diet drinks increase the risk for atrial fibrillation, we need more research “to understand all potential variables, like health conditions, body weight, physical activity, and other dietary habits,” says Prest.

Diet soda is linked to cancer

In July 2023, after reviewing research on humans and animals, the World Health Organization (WHO) added aspartame, a common ingredient in diet soda, to a list of ingredients that are “possibly carcinogenic in humans.” That might sound worse in theory than it does in practice: the WHO concluded that a person who weighs about 150 pounds can safely drink about eight cans of aspartame-sweetened diet soda per day.

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Even with this designation, aspartame isn’t necessarily carcinogenic, says Schuval. “We must keep in mind that correlation does not necessarily imply causation,” he says, and the existing research isn’t conclusive. 

Other research has found potential links from diet soda to cancers including colon, uterine, kidney, and pancreatic. But instead of diet soda being the culprit, weight gain may be, says Schuval. 

Diet soda is linked to weight gain

Artificial sweeteners like aspartame, sucralose, and saccharin are much sweeter than sugar and may alter sweet-taste receptors in your body. Some experts think that this can cause changes to your body’s hunger and satiety hormones, leading you to eat and drink more than you otherwise would. The theory isn’t a slam dunk, however. “While this change has been commonly reported in animal studies, human-based studies have had inconsistent results,” says Prest. 

Another possibility is that both sugars and artificial sweeteners can disrupt the healthy balance of gut bacteria in the GI tract, which may lead to the development of insulin resistance and Type 2 diabetes, says Prest. This, too, is hard to prove in studies, and ones that point to this pathway are often small and inconclusive, says Leah Reitmayer, a dietitian in Sanford, N.C.

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As is the case with much nutrition research, the associations found between diet soda and weight gain (and obesity) may be red herrings. “The research shows that more obese individuals drink diet soda than regular—but also eat more food than healthy weight adults,” says Reitmayer. More research is necessary to determine if diet soda is making people gain weight, or if the relationship is complicated by other factors. 

What to make of all this research

Overall, the findings are mixed, leading to bewilderment among consumers about whether diet soda is a safe beverage. 

Swithers believes we still have more questions than answers. While she says she feels persuaded by a true link between diet soda and Type 2 diabetes,  the evidence for artificial sweeteners contributing to cancer and heart disease is less clear, she says. “It just comes down to what explains that relationship,” says Swithers. Are people who choose to drink diet soda already at higher risk for certain health conditions? Are all artificial sweeteners the same? Is there another variable scientists aren’t looking at? 

“That’s where it gets really muddy,” she says. Unfortunately, we’ll have to wait to get a fuller picture of diet soda’s health effects.

Is diet soda at least better for you than regular soda?

If you routinely drink sugary sodas, all experts would rather you switch to water (naturally). But barring that, many would prefer you drink diet. “Some people find that artificially sweetened beverages help them have better control of their blood sugar,” says Prest.

Another reason is we have much more persuasive evidence of the harms of excess sugar than we do for artificial sweeteners. Over many years, research has linked sugar to conditions like obesity, inflammation, heart disease, metabolic syndrome, insulin resistance, Type 2 diabetes or worsening of prediabetes, weight gain, and tooth decay, and some studies have even indicated that reducing added sugar in the U.S. food supply could save money and lives.

It’s also important to consider what else your diet soda might be replacing. Dan DeBaun, a 32-year-old public relations manager in Minnetonka, Minn., uses diet soda as a tool to cut back on alcohol. “I never drank much alcohol previously, but I wanted to cut back even more after more studies emerged about the negative health impacts,” he says. After a successful “dry October,” where he abstained from alcohol completely, he realized he still liked having something to drink when he was out with friends or at a sporting event or concert. So he’d order a Diet Coke or Diet Pepsi.

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“Diet soda doesn't necessarily make me feel great while I'm drinking it, but I consider it a net positive compared to alcoholic beverages,” says DeBaun. “I'd only drink one, but I found having it was a good substitute.”

And dentally speaking, diet soda does clearly trump regular. “One benefit of artificial sugars is their role in reducing dental caries,” says Prest. “When sugar-sweetened beverages are exchanged for artificially sweetened beverages, the risk of developing dental caries or cavities is reduced,” she says, and this is due to the reduction in the growth of bacteria that cause them.

How to limit your diet-soda intake—or quit it altogether

Few among us can give up a hard-core diet-soda habit cold turkey, but there’s still plenty you can do to cut back, Swithers says. 

Dump it down the drain (really)

People typically think they need more of a food or drink to feel satisfied than they actually do. If you simply crave the taste of diet soda, open a can or bottle, take a few sips, and dump the rest down the sink. You might find your craving is satisfied after only a few gulps. “Drinking just a little bit, then stopping and thinking about whether you even want more soda, could be a helpful step to reducing consumption,” Swithers says.

Treat your diet soda like candy

Instead of thinking about your diet soda as a drink, think about it as candy, suggests Swithers. That way, it might start to seem ludicrous to have one with meals. “Most adults wouldn’t open a bag of candy and pour it onto their dinner plate,” she says. “Just because it’s in a glass doesn’t make it magic in some way. Would you pour a bag of jelly beans as a side dish with your meal?”

Disguise your water 

A lot of people drink diet soda because they don’t like the taste of water. To give a glass of water an appealing flavor, drop in some frozen fruit (especially the kind that releases juice, like pineapple, strawberries, and mango). Using seltzer instead of still water will make it feel even more like the bubbly treat you love.